Bigjoe, do you have an electronic crossover, or does the tweeter panel have a crossover built-in? You can damage tweeters by running a full-range signal into them without a crossover. At the very least it won't sound good, even if they're not damaged.
Generally, for biamping, the setup would be preamp to electronic crossover, then the crossover would drive each power amp. You wouldn't need a Y adapter.
Generally, for biamping, the setup would be preamp to electronic crossover, then the crossover would drive each power amp. You wouldn't need a Y adapter.